1 Tights/Bare legsBritish summer fashion is a kind of collective madness. From about early May – even if, as with this year, it is actually still slippers-in-the-morning weather – we all have to dress as if going to a picnic. Wearing black opaque tights in summer, even if the skies are gunmetal, marks your card as a killjoy and a wuss. Hey, I don't make the rules, OK? Deal with it. This, my friends, is why God invented cropped trousers. Unflattering they may be, but think of them like stabilisers while you adjust to getting your legs out, and pray that 20 minutes a week in the gym doing half-hearted lunges while watching MTV will get you Gwyneth Paltrow's legs.

2 PlaysuitsAwful name. Sounds as if the wearer should be banging a rattle on the table while covered in ketchup. But then, in America they call these rompers, which is worse. Absolutely nothing wrong with a playsuit, so long as you realise it is entirely impossible to convey the smallest amount of authority while wearing one. And no, banging the rattle harder won't help..

3 SunglassesDeciding which sunglasses to buy is simple. First question: are you the sort of person who remembers to put your sunglasses back in the case and back in your bag when you take them off. Second: do you cultivate friendships with the sort of people who will surreptitiously check out the side of your sunglasses to find out the designer label? Third: is your self-esteem affected by the name inscribed on the plastic arm by your ear? Unless you answered yes to all three questions, put a £20 cap on the purchase and buy yourself something useful with the difference.

4 Harem pantsIt's tough, keeping up with fashion. You'd think wearing unflattering trousers would be enough, but no: you also need to wear the right kind of unflattering trousers. And so it was that at the precise moment in 2007 when skinny jeans reached their tipping point – probably when you started wearing them – the fashion-forward abandoned them in favour of a new type of ridiculous trousers. The harem pant was first launched as the drop-crotch trouser, a style that mimics the effect of a toddler with a soggy nappy. Even fashionistas, it turns out, have some self-respect, and the drop-crotch was refined into the harem pant. The moment you start wearing them, the cool people will stop, so why bother?

5 Maxi dressesThe further a hem gets from the knee, the more difficult it is to wear. It makes surprisingly little difference if the direction is going up or down. If it works, a maxi dress might give you that insouciant Angelina Jolie look, without even having to shave your legs. If it doesn't, you will look like Matron from an Enid Blyton book. To err on the side of Jolie, remember the golden mantra of impact: shoes and hair. Repeat after me: shoes and hair. Shoes and hair. Got it?

6 Holiday packingMost people spend too much time and money buying new clothes for their holiday, and not enough time packing the actual suitcase. The packing has as much impact, and is cheaper, although admittedly is less fun. This is the time to indulge your inner fashion nerd: lay out everything in outfits. Allow sufficient time, and come back a couple of hours later to reassess – there will always be at least one thing that you realise instantly you won't actually wear.

7 Clogs/SandalsThe only positive benefit of the return of clogs to fashion is that, by comparison, they make gladiator sandals seem both flattering and comfortable. Gladiator sandals are, of course, neither flattering nor comfortable: they make all but the most photogenic of feet look like slabs of undercooked meat, and the law of averages states that if you crisscross a hot pair of feet with 14 leather straps, then at least one of those straps is going to rub. But the alternative, this summer, is to wear clogs. Oddly, there is nothing that accentuates a tree trunk leg quite like attaching a log to the sole of your foot.

8 SwimwearThe only sensible way to choose swimwear is to ignore all photographs posed on models. Buying a bikini because it looks good on Lara Stone is no different from buying a pair of earrings because they look good on her. It's not your fault; the presence of a to-die-for body on the page messes with the balance of your brain. It's a proven fact.

9 Summer weddingsIt is your duty as a wedding guest to look nice. Not look nice as in look attractive, but look nice as in look as if you are nice. The point of a wedding, you see, is that the bride gets to act out her perfect married-life scenario, to be the best-looking girl, the centre of attention, surrounded only by guests who will gush and whoop and give her presents and tell her husband how marvellous she is. And why not? It's one day – give the girl a break. Your role is to look decorative in the album and add to the aura of wholesome, cupcakey gorgeousness. Any fashion that hints at negativity (wonky Belgian avant-garde charcoal raw-edged felt tunic) or potentially-threatening-to-the-smug-married-order vampishness (Versace slit-to-the-thigh numbers à la Hurley) are strictly verboten.

10 Tribal trendWearing "ethnic" is sartorial code for, "I am much too serious to bother myself with fashion. I choose jewellery that looks a bit like something you'd find in an obscure gallery of the British museum to show how cultured I am. My female friends wear artisan scarves and consider themselves evolutionarily superior to women who wear diamanté." The tribal trend is an attempt by fashion designers to combat this. Good luck with that.